The nerve endings of vampire bat noses contain a sensitive, heat-detecting molecule called TRPV1. It functions like an infrared detector, directing the bats to the area of an animal's skin where blood is closest to the surface. Humans also have TRPV1 — it's in the pain-sensing nerves that detect capsaicin in spicy foods and cause the agony of sunburn.

So how long before we hack our pain sensors into infrared detectors?

While you're waiting for that, I'm going to leave this wonderfully written description of how vampire bats hunt, from the researchers who discovered the TRPV1 in bat noses:

Like other bats, they feed only at night, and they have excellent eyesight enhanced by acute hearing and an ability to emit high-pitched sounds that help them navigate. Their teeth lack enamel, which keeps them constantly razor sharp and allows them to delicately tear through the hide of a sleeping animal without waking it. Grooves in their tongue draw up the blood seeping through the open wound through capillary action, and they have anticoagulation chemicals inside their saliva to keep it flowing.

Within minutes of sinking its teeth in an animal's flesh, an adult vampire bat can drink half its body weight in blood. But first they must find a vein, helped by it's a major adaptations: heat-sensing ability, which allows them to "see" a vein at night.